1. Field of the Invention
The invention relates to a method and apparatus for effecting the opening and closing of a well conduit extending to a downhole tool to permit the injection of predetermined amounts of treating fluid down the conduit to the downhole tool at a preselected rate.
2. History of the Prior Art
Many producing wells have low fluid levels, i.e., the levels of fluid in the casing annulus surrounding the production conduit does not extend upwardly from a production zone to any substantial extent, hence the hydrostatic fluid pressure in the production conduit will always substantially exceed the fluid pressure existing in the casing annulus.
This presents a problem when it is desired to treat a production formation, or a portion thereof, with chemicals conventionally employed to enhance the productivity of wells. The perforation treating apparatus may be positioned so as to straddle a selected portion of the production zone and provide a fluid passage to such selected portion from the tubular work string or the production conduit. However, if it is only desired to inject a limited amount of chemical treating fluid at a selected rate of flow into the selected portion of the production zone, this becomes a matter of some difficulty since the low fluid pressure existing in the production zone would effectively rapidly drain any quantity of treating fluid contained in the tubular string. There is, therefore, a definitive need for an injection control valve which may be positioned in the tubular string conduit immediately above the downhole tool and controlled from the well surface to selectively open and close such conduit so as to permit only a predetermined amount of treating fluid to be supplied to the selected portion of the production zone being treated at a predetermined rate of flow. Injection control valves for this purpose have been known in the prior art, but have employed either springs or fluid pressures to shift the valve between its open and closed positions. This necessarily means that careful adjustment of the valve must be made before it is lowered into the well, in order to insure that the valve will function under the pressure conditions existing at the downhole location where the valve is positioned. Since these conditions are never known with great accuracy, this means that much intelligent guessing has to be made with respect to the proper amount of spring force or the proper amount of fluid pressure required to insure the reliable operation of the injection valve from its closed to its open position for the required duration.
Additionally, prior art injection control valves have not incorporated means for establishing a predetermined rate of flow of chemical treatment fluid into the production zone being treated.